1. Field of the Invention
The present invention is directed to a method and device for treating congestive heart disease and related valvular dysfunction. More particularly, the invention provides a cardiac support device with sections having variable compliance.
2. Description of the Prior Art
Congestive heart disease is a progressive and debilitating illness. The disease is characterized by a progressive enlargement of the heart.
As the heart enlarges, the heart is performing an increasing amount of work in order to pump blood each heart beat. In time, the heart becomes so enlarged the heart cannot adequately supply blood. An afflicted patient is fatigued, unable to perform even simple exerting tasks and experiences pain and discomfort. Further, as the heart enlarges, the internal heart valves cannot adequately close. This impairs the function of the valves and further reduces the heart's ability to supply blood.
Causes of congestive heart disease are not fully known. In certain instances, congestive heart disease may result from viral infections. In such cases, the heart may enlarge to such an extent that the adverse consequences of heart enlargement continue after the viral infection has passed and the disease continues its progressively debilitating course.
Patients suffering from congestive heart disease are commonly grouped into four classes (i.e., Classes I, II, III and IV). In the early stages (e.g., Classes I and II), drug therapy is the commonly prescribed treatment. Drug therapy treats the symptoms of the disease and may slow the progression of the disease. Importantly, there is no cure for congestive heart disease. Even with drug therapy, the disease will progress. Further, the drugs may have adverse side effects.
Presently, the only permanent treatment for congestive heart disease is heart transplant. Heart transplant procedures are very risky, extremely invasive and expensive and only shortly extend a patient's life. Furthermore, not enough hearts are available for transplant to meet the needs of congestive heart disease patients and many patient's do not qualify for heart transplant for failure to meet any one of a number of qualifying criteria.
Substantial effort has been made to find alternative treatments for congestive heart disease. Recently, a new surgical procedure has been developed. Referred to as the Batista procedure, the surgical technique includes dissecting and removing portions of the heart in order to reduce heart volume. This is a radical new and experimental procedure subject to substantial controversy. Furthermore, the procedure is highly invasive, risky and expensive and commonly includes other expensive procedures (such as a concurrent heart valve replacement). Also, the treatment is limited to Class IV patients and, accordingly, provides no hope to patients facing ineffective drug treatment prior to Class IV. Finally, if the procedure fails, emergency heart transplant is the only available option.
Clearly, there is a need for alternative treatments applicable to both early and later stages of the disease to either stop the progressive nature of the disease or more drastically slow the progressive nature of congestive heart disease. Unfortunately, currently developed options are experimental, costly and problematic.
Cardiomyoplasty is a recently developed treatment for earlier stage congestive heart disease (e.g., as early as Class III dilated cardiomyopathy). In this procedure, the latissimus dorsi muscle (taken from the patient's shoulder) is wrapped around the heart and chronically paced synchronously with ventricular systole. Pacing of the muscle results in muscle contraction to assist the contraction of the heart during systole.
While cardiomyoplasty has resulted in symptomatic improvement, the nature of the improvement is not understood. For example, one study has suggested the benefits of cardiomyoplasty are derived less from active systolic assist than from remodeling, perhaps because of an external elastic support. The study suggests an elastic support (i.e., a non-stimulated muscle wrap or an artificial elastic sock placed around the heart) could provide similar benefits. Kass et al., Reverse Remodeling From Cardiomyoplasty In Human Heart Failure: External Support Versus Active Assist, 91 Circulation 2314–2318 (1995).
Even though cardiomyoplasty has demonstrated symptomatic improvement, studies suggest the procedure only minimally improves cardiac performance. The procedure is highly invasive requiring harvesting a patient's muscle and an open chest approach (i.e., sternotomy) to access the heart. Furthermore, the procedure is expensive—especially those using a paced muscle. Such procedures require costly pacemakers. The cardiomyoplasty procedure is complicated. For example, it is difficult to adequately wrap the muscle around the heart with a satisfactory fit. Also, if adequate blood flow is not maintained to the wrapped muscle, the muscle may necrose. The muscle may stretch after wrapping reducing its constraining benefits and is generally not susceptible to post-operative adjustment. Finally, the muscle may fibrose and adhere to the heart causing undesirable support on the contraction of the heart during systole.
In addition to cardiomyoplasty, mechanical assist devices have been developed as intermediate procedures for treating congestive heart disease. Such devices include left ventricular assist devices (“LVAD”) and total artificial hearts (“TAH”). An LVAD includes a mechanical pump for urging blood flow from the left ventricle and into the aorta. An example of such is shown in U.S. Pat. No. 4,995,857 to Arnold dated Feb. 26, 1991. LVAD surgeries are still in U.S. clinical trials and not generally available. Such surgeries are expensive. The devices are at risk of mechanical failure and frequently require external power supplies. TAH devices, such as the celebrated Jarvik heart, are used as temporary measures while a patient awaits a donor heart for transplant.
Other attempts at cardiac assist devices are found in U.S. Pat. No. 4,957,477 to Lundbäck dated Sep. 18, 1990, U.S. Pat. No. 5,131,905 to Grooters dated Jul. 21, 1992 and U.S. Pat. No. 5,256,132 to Snyders dated Oct. 26, 1993. Both of the Grooters and Snyders patents teach cardiac assist devices which pump fluid into chambers opposing the heart to assist systolic contractions of the heart. The Lundbäck patent teaches a double-walled jacket surrounding the heart. A fluid fills a chamber between the walls of the jacket. The inner wall is positioned against the heart and is pliable to move with the heart. Movement of the heart during beating displaces fluid within the jacket chamber.
Commonly assigned U.S. Pat. No. 5,702,343 to Alferness dated Dec. 30, 1997 teaches a jacket to constrain cardiac expansion during diastole. The present invention pertains to improvements to the invention disclosed in the '343 patent.